Cal. VEH § 21360

Local authorities in their respective jurisdictions may, within the reasonable exercise of their police power and subject to Section 21353, place and maintain official traffic control devices to regulate traffic at the intersection of a highway and a private road or driveway. Official traffic control devices may be erected at or near such intersection, except no such device shall be erected upon a private road or driveway without consent of the owner thereof. When official traffic control devices are installed and in operation, the private road or driveway shall be deemed a highway only for the purpose of determining the existence and location of an intersection.